Current electronic equipment uses semiconductor devices such as, for example, memory devices and processing devices. For example, mobile electronic products such as, for example, digital cameras, portable digital assistants, portable audio/video players and mobile terminals continue to require mass storage memories, preferably non-volatile memory with ever increasing capacities and speed capabilities. Non-volatile memory and hard disk drives are preferred since data is retained in the absence of power, thus extending battery life.
While existing memory devices operate at speeds sufficient for much current consumer electronic equipment, such memory devices may not be adequate for use in future electronic products and other products where high data rates are desired. For example, a mobile multimedia device that records high definition moving pictures is likely to require a memory module with a greater programming throughput than one with current memory technology. While such a solution appears to be straightforward, there is a problem with signal quality at such high frequencies, which sets a practical limitation on the operating frequency of the memory. The memory communicates with other components using a set of parallel input/output (I/O) pins, the number of which depends on the desired configuration. The I/O pins receive command instructions and input data, and provide output data. This is commonly known as a parallel interface. High-speed operation may cause deleterious communication effects such as, for example, cross-talk, signal skew and signal attenuation, which degrade signal quality.
In order to incorporate higher density and faster operation on the system boards, there are two design techniques possible: multi-drop and serial interconnection configurations. In the multi-drop configuration, a plurality of memories is connected in-parallel to a controller. In the serial interconnection configuration, a plurality of memories is connected in-series. These design techniques may be used to overcome the density issue that determines the cost and operating efficiency of memory swapping between a hard disk and a memory system. However, multi-drop configurations have shortcomings relative to serial interconnection configurations of memory systems. For example, if the number of multi-drop memory systems increases, as a result of the loading effect of each pin, the delay time also increases so that the total performance of multi-drop is degraded by the parallel connections caused by the wire resistor-capacitor loading and the pin capacitance of the memory device. In serial interconnection configurations, control command bits, address bits, and data bits may be effectively provided through the series-connections. In the interconnection configuration, each device may have to be identified by a device identifier or a device address to operate or to respond to the controller.